The present invention relates to a hydraulic barrier for use in sealing the perimeter of, in particular, landfill sites, most particularly, municipal solid waste sites.
One of the biggest problems to be addressed with regard to municipal solid waste (MSW) landfills is the migration of leachate from within the landfill to the surrounding land. Leachate is liquid which has percolated through the solid waste or other medium and has extracted from it, dissolved or suspended materials, which may include potentially harmful material. In the United Kingdom alone, approximately 120 million tonnes of controlled waste, including 20 million tonnes of domestic waste, are dumped in MSW landfills every year.
In the past, one of the most common means of preventing leaching from landfill sites was to line the landfill with high density polyurethane (HDPE) sheeting, thereby providing a waterproof barrier about the boundary of the site. However, one major problem associated with such a system is that, once punctured, the HDPE sheeting becomes ineffective at that location. Furthermore, such HDPE sheeting is extremely susceptible to such puncturing, and in addition, the overlapping edges of adjacent HDPE sheets must be welded together in order to prevent the migration of leachate from therebetween.
Geosynthetic clay liners (GCL""s) are widely employed in landfill barrier systems. A GCL is a relatively thin layer of processed clay, preferably bentonite, which is either fixed between two sheets of geotextile or bonded to a geomembrane. A geotextile is a woven or nonwoven material which is largely impervious to liquid, and is also largely resistant to penetration damage. A geomembrane is a polymeric sheet material that is impervious to liquid. Bentonite, a granular clay formed from volcanic ash, is extremely absorbent, and attracts positively charged water particles. Therefore, once exposed to liquid (water or leachate), bentonite rapidly hydrates, causing swelling, which gives the clay the ability to self heal holes in a GCL. The quality of the clay used effects various characteristics of a GCL, the most important being the hydraulic conductivity (permeability) thereof. Sodium bentonite, a naturally occurring compound in a silicate clay formed from volcanic ash, provides bentonite with its distinctive property.
As a GCL hydrates, it becomes slightly flowable, which gives the GCL its self healing properties. It is therefore recommended that the side walls defining a land fill site are formed with a gradient of no greater than approximately 30xc2x0 from the horizontal, if same are to be lined with a GCL. This is due to the fact that the loading on a GCL, if disposed at a steeper gradient, may result in unacceptable deformation of the GCL, which could compromise the integrity thereof. The loading results from the force acting on the GCL as a result of its own dead weight, in addition to the weight of the refuse or other matter sitting thereon. This therefore means that a substantial volume at the perimeter of each landfill must be surrendered in order to include such sloping side walls, thereby significantly decreasing the capacity of the site.
It is therefore an object of the present invention to maximise the capacity of a landfill site.
It is a further object of the present invention to provide a hydraulic barrier which is relatively inexpensive and easy to install, and which can furthermore be transported with ease.
It is a still further object of the present invention to provide a hydraulic barrier which enables the at least partial decontamination of material contained, by the hydraulic barrier, in a landfill site or the like.
It is a still further object of the present invention to provide an improved hydraulic barrier which utilises a GCL.
The present invention therefore provides a hydraulic barrier comprising a geosynthetic clay liner; characterised in that a support frame is provided, the support frame being adapted and arranged to support the geosynthetic clay liner in a substantially vertical orientation.
Preferably, the geosynthetic clay liner comprises sodium bentonite.
Preferably, the support frame comprises a pair of spaced apart support frame members, the geosynthetic clay liner being located between said pair of support frame members.
Preferably, each support frame member is urged or pressed into face to face engagement with the geosynthetic clay liner in order to apply pressure thereto.
Preferably, the support frame further comprises a pair of spaced apart outer members between which the pair of support frame members and the geosynthetic clay liner are located.
Preferably, a cavity is defined between the outer member and the support frame member on each side of the geosynthetic clay liner, each cavity being filled with a granular material, most preferably pea gravel.
Preferably, the pair of support frame members are substantially reticulated.
Preferably, each outer member is connected to the corresponding support frame member by means of a plurality of struts extending therebetween.
Preferably, each outer member is provided with a lining, preferably a geotextile lining, most preferably a non-woven geotextile lining.
Preferably, each strut is hingedly connected to the respective support frame member and to the respective outer member.
Preferably, each outer member is further connected to the corresponding support frame member by means of a plurality of braces, the braces being hingedly connected to the respective support frame member and to the respective outer member.
In one embodiment of the invention, the hydraulic barrier comprises a pair of spaced apart geosynthetic clay liners, each of which is supported in a substantially vertical orientation by the support frame.
Preferably, the support frame comprises two pairs of support frame members, each geosynthetic clay liner being located between a respective one of said two pairs of support frame members.
Preferably, the pair of geosynthetic clay liners define a core therebetween, within which core may be collected any leachate which passes through either geosynthetic clay liner into the core.
Preferably, the core is filled with a granular material.
Preferably, the core, once filled with the granular material, is further filled with a liquid into which the leachate may be entrained.
Preferably, the liquid may be withdrawn from the core to permit the decontamination thereof.
Preferably, the decontaminated liquid may be returned to the core.
Preferably, the liquid and/or granular material within the core is adapted for the bioremediation of at least a portion of the leachate within the core.
Preferably, the liquid within the core has a greater pressure head than the leachate located externally of the core.
Preferably, the support frame is collapsible to facilitate the transport and/or storage of the hydraulic barrier.
As used herein, the term xe2x80x9cgeosynthetic clay liner (GCL)xe2x80x9d is intended to mean a layer of processed clay such as, but not limited to, bentonite, which layer of clay is preferably maintained between a pair of outer sheets, or similar substrates, such as geotextiles, which are substantially impervious to penetration by both liquids and solid materials, thereby forming a composite structure with the layer of clay, the GCL thus having an extremely low hydraulic conductivity, preferably in the range of 1xc3x9710xe2x88x9212 m/sec to 1xc3x9710xe2x88x9214 m/sec for landfill leachate, diesel, oil, petrol, etc.
As used herein, the term xe2x80x9creticulatedxe2x80x9d is intended to mean being formed substantially from apertures, such as to form a mesh.
As used herein, the term xe2x80x9centrainedxe2x80x9d is intended to mean the action of one liquid becoming mixed with another, whether the two liquids are miscible or not.
These and other objects, advantages, purposes and features of this invention will become apparent upon review of the following specification in conjunction with the drawings.